The term "pathological hydrophobic interactions" means detrimental adhesion of components, including but not limited to, cells and molecules in blood or other biological fluids thereby slowing or stopping the flow of blood or other biological fluid. The term "fibrinolytic enzyme" means any enzyme that is capable of cleaving fibrin or capable of causing fibrin to be cleaved. Enzymes that are capable of cleaving fibrin or causing fibrin to be cleaved include, but are not limited to, streptokinase, urokinase, tissue plasminogen activator (t-PA) produced from cell cultures, tissue plasminogen activator produced by recombinant DNA technology and plasminogen activator produced from prourokinase. The terms "isotonic" or "isoosmotic" solution are defined as solutions having the same osmotic pressure as blood. The term "SOD" means superoxide dismutase and refers to any enzyme capable of neutralizing oxygen radicals. The terms clot, fibrin clot and thrombus are used interchangeably. The term "microcirculation" means blood circulation through blood vessels that are about 50 microns in diameter or less. The term "soluble fibrin" means soluble high molecular weight polymers of fibrinogen and fibrin. The term "biological fluids" means blood, lymph, or other fluids found in animals or humans. The term "platelet suspension" means a suspension of platelets that has a higher concentration of platelets than that found in blood. The term "plasma extender" means any substance that can be added to animal or human blood to maintain or increase coloid osmotic pressure. The term "cytoprotective" as used herein, means an increased ability of myocardial, endothelial and other cells to withstand ischemia or recover from ischemia, or other noxious insults including but not limited to burns. The term "ischemic tissue" is any tissue that is damaged from reduced blood flow. The term "anticoagulant" is any compound or agent that inhibits the blood coagulation process. The term "reperfusion injury" means injury to tissue or cells which occurs during reperfusion of damaged tissue with blood. The term "damaged tissue" means tissue damaged by ischemia, burns, toxins or other noxious insult.
It is to be understood that the citation of art contained herein is in no way to be construed as an admission that said art is suitable reference against the present patent application nor should this citation act as a waiver of any rights to overcome said art which may be available to the applicant.
A number of reports have described high amounts of fibrinogen and/or soluble fibrin in the blood of patients with thrombosis, impending thrombosis and many other diseases. These conditions include acute or chronic infection, severe trauma, burns, sickle cell crisis, malaria, leukemia, myocardial infarction, sepsis, shock, and almost any serious illness which produces tissue damage or surgical maneuvers. Evidence indicates that the high concentrations of fibrinogen and/or soluble fibrin may play an important role in the pathology of the conditions. Furthermore, much of the pathology that is encountered in disease may be due to pathological hydrophobic interactions which may be at least partially mediated by high concentration of fibrinogen and/or soluble fibrin.
What is needed is a means of decreasing the adverse effects of soluble fibrin. This would involve blocking the adhesion of soluble fibrin to cells in the circulation thereby blocking the aggregation of such cells and their adhesion or friction to vessel walls in the microvasculature. This would also decrease the risk of thrombosis.
Each year about 550,000 Americans die from heart attacks. Even more--close to 700,000--have heart attacks and live. While a heart attack victim may survive, part of his or her heart will almost certainly die. The death of heart muscle, called myocardial infarction, is due to coronary artery thrombosis in 70-90% of the cases. When a thrombosis, or blood clot, occludes one of the arteries of the heart, it stops the flow of blood to the surrounding muscle which deprives it of oxygen and other nutrients. In the past, nothing could be done to reverse this process. The high technology devices in intensive care units mostly support patients so they can live while a portion of their heart dies.
Similar situations occur in many other tissues when the blood supply to the tissue is affected by a thrombus or embolus. Stroke, deep vein thrombosis and pulmonary embolus are examples. Typically, the clot forms and is not treated for a relatively long period of time. Blood flow distal to the clot is greatly diminished or is stopped completely. The tissue that is normally fed by that vessel will be severely damaged unless blood flow is reestablished in a short period of time.
It has been found that certain enzymes are able to degrade, initiate or activate other enzymes that can degrade fibrin deposits to open clogged arteries. The enzymes which have been used successfully include streptokinase, urokinase, prourokinase, tissue plasminogen activator produced from cell cultures and tissue plasminogen activator produced by recombinant DNA technology. These enzymes are most successful if administered shortly after the occlusion of the blood vessels before the heart tissue has sustained irreversible damage. In one study of 11,806 patients treated with intravenous or intracoronary artery streptokinase, an 18% improvement of survival was demonstrated. If the treatment was begun within one hour after the initial pain onset of the heart attack, the in-hospital mortality was reduced by 47%. (See The Lancet, Vol. 8478, p. 397-401, Feb. 22, 1986). It was demonstrated that early lysis of the thrombus resulted in salvage of a portion of heart tissue which would have otherwise have died. In studies using angiography to assess the patency of blood vessels, it was found that tissue plasminogen activator could completely open the vessels of 61% of the 129 patients versus 29% of controls who were not treated with the enzyme. (See Verstraete, et al., The Lancet, Vol. 8462, p. 965-969, Nov. 2, 1985). Tissue plasminogen activator requires the addition of approximately 100 .mu.l of Tween 80 per liter of solution to promote dispersion of the enzyme. (See Korninger, et al., Thrombos, Haemostas, (Stuttgart) Vol. 42(2), p. 561-565 (1981)).
The natural enzymes that lyse thrombi in vessels do so by activating fibrinolysis. Fibrin is the protein produced by polymerization of fibrinogen. It forms a gel which holds the thrombus together. The fibrin molecules which form clots gradually become cross-linked to make a more stable clot. All three enzymes, urokinase, streptokinase and tissue plasminogen activator, are effective because of their ability to activate an enzyme, plasmin, which degrades fibrin. Thus, they have similar effects on fibrin but they have different toxicities. If the fibrinolytic mechanisms (i.e., plasmin) are activated in the vicinity of a clot, the clot is lysed. If, however, they are activated systemically throughout the circulation, the body's capacity to stop bleeding or hemorrhage is markedly reduced. Streptokinase and urokinase tend to activate systemic fibrinolysis. Consequently, they have been most effective when injected directly into the affected blood vessel.
Tissue plasminogen activator or t-PA, in contrast, becomes effective only when it is actually attached to fibrin. This means its activity is largely localized to the immediate area of a clot and does not produce systemic fibrinolysis. For this reason, tissue plasminogen activator is thought to produce less risk of hemorrhage than the other enzymes. If high doses are used in an effort to increase the rate of clot lysis or to lyse refractory clots, then the amount of systemic fibrinolysis and risk of hemorrhage can become significant. t-PA can be injected intravenously into the general circulation. It circulates harmlessly until it contacts the fibrin in a blood clot where it becomes activated and causes the lyses of the clot. Tissue plasminogen activator is able to cause the lysis of a clot which is extensively cross-linked. This means it is possible to lyse clots which have been present for many hours.
Remarkable as the new enzyme therapies are, they are subject to serious complications and are not effective in all patients. Clots in the anterior descending branch of the left coronary artery are much more readily lysed than those in other arteries. If the enzyme is not delivered by the blood stream directly to the thrombus, it has no effect. For various reasons, more blood passes by or trickles around thrombi in the left anterior descending coronary artery than in the other major arteries. In addition, the presence of collateral circulation which forms in response to compromised blood flow in the major arteries adversely affects the rate of reopening or recanalization of the thrombosed major arteries. It is thought the presence of many collateral vessels which allow blood to bypass the clot reduces the pressure gradient across the clot. This in turn reduces the blood flow through the tiny openings which may persist in the clot, impedes the delivery of enzymes to the clot, and prevents the clot from being lysed.
Even after the clot has been lysed, the factors which led to the formation of the thrombus persist. This produces a high incidence of re-thrombosis and further infarction in the hours and days following lysis of the clot. Rethrombosis has been reported in between 3% and 30% of cases in which the initial treatment successfully lysed the clot. Anticoagulants are currently used to prevent the formation of new thrombi, but they tend to induce hemorrhage. There is a delicate balance between the amount of anticoagulation necessary to prevent re-thrombosis of the vessels and that which will produce serious hemorrhage.
A reported advantage of t-PA is its short half-life of less than 10 minutes, which may allow rapid reversal of bleeding problems should they occur. However, the clinical value of this consideration has not yet been demonstrated. Moreover, the short half-life may lead to an increased reocclusion rate following discontinuation of thrombolytic therapy, (See Williams, D. O., et al., "Intravenous recombinant tissue-type plasminogen activator in patients with acute myocardial infarction: a report from the NHLBI Thrombolysis in Myocardial Infarction Trial.", Circulation 1986;73:338-46). To counter this problem, t-PA infusions have been continued for up to 6 hours in phase II of the TIMI (Thrombolysis in Myocardial Infarction Trial). Whether this will effectively reduce the incidence of reocclusion without increased bleeding remains to be proven. Although active thrombolysis ceases shortly after discontinuing administration of t-PA, it takes several hours to replace fibrinogen, so that the risk of continued bleeding does not terminate when t-PA is stopped. (See Rich, M. W., "tPA: Is it worth the price?", American Heart Journal, 1987, Vol 114:1259-1261
Finally, dissolving the clot after irreversible damage has taken place has little effect. The irreversible damage could be either to the heart muscle or vascular bed of the tissue supplied by the blood vessel. Once a cell is dead, the change is irreversible. However, the term irreversible damage is frequently applied to tissue in which a chain of events leading to cell death has been initiated, even though most cells are not yet dead. If this chain of events were broken, for example by restoring the microvasculature blood supply or stabilizing fragile membranes, then many cells could be saved. A major problem in widespread implementation of this new enzyme therapy is to find ways of identifying and treating the patients earlier in their disease and to find ways to make the treatment effective for a longer period of time after the initiation of thrombosis.
Animal studies have provided a better understanding of the events which control blood flow and tissue death following coronary artery thrombosis. Much of the heart muscle receives blood from more than one vessel. For this and other reasons, the tissue changes following a coronary thrombosis are divided into distinct zones. The central zone of tissue, i.e., usually that zone of tissue closest to the thrombus, becomes almost completely necrotic. This is surrounded by an area of severe ischemia. Outside this is an area of lesser ischemia called the marginal zone. Finally, there is a jeopardized zone which surrounds the entire area.
In studies with baboons, the central necrotic area was not affected by recanalization of the vessel after several hours. However, muscle in the other zones which had undergone less severe damage during the ischemic period could be salvaged. A surprising finding was that lysing of the thrombus to produce a perfect arteriograph was insufficient to restore normal flow in the majority of animals. (See Flameng, et al, J. Clin. Invest., Vol. 75, p. 84-90, 1985). Some further impediment to flow had developed in the area supplied by the vessel during the time that it was occluded. In further studies, it was demonstrated that immediately after removing the obstruction to the vessel, the flow through the damaged tissue began at a high rate. However, within a short time the blood flow through the ischemic zone decreased and the tissue died.
Consequently, the regional blood flow immediately after reperfusion is a poor predictor of the salvage of myocardial tissue. If the blood flow through the damaged tissue remained near the normal levels, the success of tissue salvage was much greater. Hemorrhage occurred almost exclusively in the severely ischemic zone reflecting damage to the small blood vessels. The hemorrhage, however, remained limited to the severely ischemic tissue and did not cause extension of the infarction or other serious complication. Therapies which could preserve the blood flow through the small blood vessels distal to the major area of thrombus after reperfusion could be expected to markedly increase the salvage of myocardial tissue.
The damage to heart muscle cells which occurs after lysing the thrombus is due to other factors as well as ischemia. Contact of fresh blood with damaged or dead cells induces the influx of neutrophils, or pus cells, which can damage or kill heart cells which would otherwise have recovered. Much of the damage caused by neutrophils has been attributed to superoxide ions. (For a general review, please see "Oxygen Radicals and Tissue Injury" Proceedings of a Brook Lodge Symposium, Augusta Michigan, Barry Halliwell, Ed.) The superoxide anion can damage tissue in several ways. The interaction of the superoxide anion with hydrogen peroxide leads to the production of hydroxyl radicals which are highly toxic and react rapidly with most organic molecules. Mannitol is a selective scavenger of hydroxyl radicals. The enzymes, superoxide dismutase, catalyzes the decomposition of the superoxide anion. Enzymes such as superoxide dismutase, free radical scavengers or agents which prevent the influx on neutrophils are able to increase the salvage of heart muscle cells.
Continuing therapy is needed even after restoration of blood flow and salvage of damaged tissue. The arteriosclerosis that caused the original heart attack remains. American and European researchers have found that arteriosclerosis still narrows the arteries in 70-80% of patients whose clots were lysed by thrombolytic therapy. Many physicians believe this obstruction must be opened for long term benefits.
Balloon angioplasty is a procedure whereby a catheter with a small balloon is inserted into the narrowed artery. The balloon is inflated, compresses the atherosclerotic plaque against the vessel wall and dilates the artery. The effectiveness of this procedure is limited by the effects of ischemia produced by the balloon, by embolization of atheromatous material which lodges in distal vessels and by an increased tendency for immediate or delayed thrombosis in the area damaged by the balloon. The balloon tears the tissue exposing underlying collagen and lipid substances which induce formation of thrombi. The thrombus may occlude the vessel immediately or set up a sequence of events which leads to occlusion many days or weeks later. In addition, there is an interruption of blood flow to the heart tissue when the balloon is inflated. When the blood flow is interrupted, tissue downstream from the balloon is deprived of blood and can be damaged. Balloon angioplasty is representative of numerous clinical and experimental procedures for repairing the lumen of diseased arteries and vessels.
What is needed is a means of rendering the surface of the dilated vessel less thrombogenic, improving the blood flow through the distal tissue and breaking the embolized material into smaller pieces which are less likely to produce embolic damage. A means of restoring blood flow through the microcapillaries downstream from the site of balloon inflation is also required.
Another area where fibrinogen/fibrin plays a role is tumors. There is now strong evidence that fibrinogen-related proteins are localized in solid tumors. The anatomical distribution of fibrin in tumors varies depending on the tumor type. In carcinomas, fibrin is deposited in the tumor stroma and around tumor nests and may be particularly abundant toward the tumor periphery and at the tumor host interface. By contrast, fibrin is often less prominent in older, more central tumor stroma characterized by sclerotic collagen deposits. Fibrin may also be found between individual carcinoma cells. In some, but not all such cases, interepithelial fibrin deposits are related to zones of tumor necrosis; however, zones of tumor necrosis are not necessarily sites of fibrin deposition. Fibrin deposition in sarcomas has been less carefully studied than that in carcinomas. In lymphomas, fibrin deposits may be observed between individual malignant tumor cells as well as between adjacent, apparently reactive benign lymphoid elements. Fibrin has been reported to appear in zones of tumor sclerosis, as in Hodgkin's disease. Research has indicated that the pattern and extent of fibrin deposits are characteristic for a given tumor. (See Hemostasis and Thrombosis, Basic Principles and Clinical Practice, "Abnormalities of Hemostasis in Malignancy", pp. 1145-1157, ed. by R. W. Colman, et al., J. B. Lippincott Company, 1987).
The lack of a uniform vascular supply to tumors can impede diagnostic and therapeutic procedures. For example, hypoxic tumors are less susceptible to many drugs and to radiation. Conventional drugs and new drugs, such as monoclonal antibody conjugates, are not effective unless they are delivered to tumor cells. Fibrin deposits that surround some types of tumors inhibit delivery of the drugs to the tumor. The blood supply of tumors is further compromised by other factors as well. Blood vessels in tumors are frequently small and tortuous. The hydrodynamic resistance of such channels further impedes the flow of blood to tumors.
Finally, lipid material on the atherosclerotic wall contributes to the bulk of the plaque which narrows the lumen of the artery and produces a highly thrombogenic surface. What is needed is a method of extracting or covering lipids from atherosclerotic plaques which leaves their surfaces less thrombogenic and reduces their bulk.
Use of copolymers prepared by the condensation of ethylene oxide and propylene oxide to treat an embolus or a thrombus has been described (See U.S. Pat. No. 3,641,240). However, the effect is limited to recently formed, small (preferably microscopic) thrombi and emboli which are composed primarily of platelets. To be effective, the compound must be used within 20 minutes after the initiation of thrombosis.
The use of the ethylene oxide and propylene oxide copolymer has little or no effect on a clot in a patient who has suffered a severe coronary infarction because such patients almost never receive treatment within 20 minutes following initiation of thrombosis. It is likely that many persons do not develop symptoms until the thrombus reaches considerable size. The clots that are occluding the blood vessel in these patients are large and stable clots. Stable clots are clots in which the fibrin has undergone cross linking. Fibrin which has undergone crosslinking is not effected by presence of the ethylene oxidepropylene oxide copolymers. The copolymers only affect new clots composed primarily of platelets in which the newly formed fibrin has not crosslinked.
Another problem that commonly occurs in damaged tissue where blood flow is interrupted is a phenomenon called "no reflow" phenomenon. This is a conditions wherein blood flow is interrupted to a tissue. When blood flow is restarted, such as after a clot is removed, flow in the smaller microcapillaries is often impaired because blood cells tend to clump in the microcapillaries thereby inhibiting flow of blood to the tissue. This can result in damage to the tissue.
In addition, such a composition would be useful in removing clots from solid tumors, increasing flow through tortuous channels and thereby allow delivery of therapeutic drugs to the tumor.
A further need is a composition that can be used to prevent or treat "no reflow" phenomenon. Such a composition should be capable of causing blood to flow in tissue after blood flow has stopped thereby preventing tissue damage.
Increased demand for platelet concentrates to treat bleeding associated with thrombocytopenia has prompted the need to determine optimal methods of storing platelets prior to transfusing them into a patient.
Viability, as measured by survival of .sup.51 Cr-labeled platelets, seems best preserved when stored at 22.degree. C., whereas platelet function, as measured by the ability of platelets to aggregate in response to epinephrine, collagen, and adenosine diphosphate is better preserved at 4.degree. C. Platelets stored at room temperature for 48 to 72 hours as well as those kept refrigerated for 24 to 48 hours have been found by different investigators to produce satisfactory increases in platelet levels when transfused to thombocytopenic patients.
Thus, blood banks wishing to store platelets prior to their transfusion into a patient are faced with the dilemma of whether they should be kept at room temperature, thus preserving their lifespan but possibly compromising their functional capacity, or whether they should be stored in the approximately 4.degree. C. with the resultant preservation of function but shortening of posttransfusion survival time.
What is needed is a composition and method which can be added to a suspension of platelets which will preserve both lifespan and function of the platelets so that the platelet suspension can be stored for longer periods of time. Such a composition should also be capable of inhibiting the aggregation or clumping of platelets in the suspension.
Finally, the present inventor has identified a phenomenon called pathological hydrophobic interactions between blood components and those cells which line the blood vessels. This phenomenon is typically encountered when tissue is damaged in some manner. These pathological hydrophobic interactions cause blood flow to be reduced or stopped thereby causing damage to surrounding tissue. What is needed is a composition and method for reducing the pathological hydrophobic interactions and thereby allowing blood to flow into the damaged tissue.